1. Field of the Invention
This invention relates to a communication control apparatus employing an xDSL technology that enables a high-speed communication of several M bits/second even when a copper wire cable is used for the subscriber line. This invention especially relates to an ADSL communication control method, communication control apparatus, and ADSL communication apparatus that performs an initialization procedure after performing a handshake procedure.
2. Description of Related Art
With the widespread use of the Internet, there is an increasing demand for a high-speed access line that can be used for a fixed connection. Optical fiber is becoming more popular in the backbone of communication industries, and gigabit class super high-speed lines are starting to be employed in the key components of the backbone. However, most of the subscriber lines that connect user's home and storage centers of the communication industries are copper wire cables that are constructed for telephones. Therefore, an introduction of the xDSL technology that enables a high-speed communication of several M bits/second with a copper wire cable has been considered.
An ADSL method is one aspect of the xDSL technology. The ADSL method uses a much higher carrier frequency range of more than 35 kHz compared to the range used for telephones (less than 4 kHz). Therefore, high-speed data communication can be performed using a telephone line, without hindering telephone functions.
FIG. 7 is a schematic illustration of a system configuration of a subscriber side. The storage center of a communication industry (center side) transmits signals to line 1. User's home (remote side) splits received signals from line 1 at splitter 2, inputting voice range signals (less than 4 kHz) into a telephone (POTS: Plain Old Telephone Service) 3, and high range signals (more than 35 kHz) into ADSL communication apparatus 4. ADSL communication apparatus 4 includes ADSL modem 5 and controller 6. Controller 6 controls data transmission/reception with data communication apparatus 7 (e.g., personal computer) and performs an initialization control for ADSL modem 5.
FIGS. 8 and 9 illustrate initialization sequence that is performed at ADSL modem 5 based on the ITU-T recommended G.992.1. In the example of FIG. 8, the control is arranged to perform a handshake procedure based on the ITU-T recommended G.994.1, prior to performing an initialization sequence.
In an initialization sequence based on the ITU-T recommended G.992.1, the center side transmits C-RATES1 and C-MSG1 to the remote side as the first negotiation, informing a general transmission speed for the downlink and uplink and additive information. In response, the remote side transmits R-RATES1 and R-MSG1 to the center side, informing the remote side's transmission speed and additive information.
After the first negotiation, both center and remote sides transmit training signals, C-MEDLEY and R-MEDLEY, so that both center and remote sides check the reception conditions and determine carriers for carrier-off and bit number used for each carrier. As a second negotiation, the remote side transmits R-RATES and R-MSG to the center side, informing the center side of the remote side's capacity information and information regarding the reception conditions (e.g., S/N). The center side determines detail information (transmission speeds for uplink and downlink) and capacity information based on the reception result of R-MEDLEY, and transmits C-RATES and C-MSG to the remote side to inform the center side's capacity information and detail information regarding the reception conditions.
After the second negotiation, the remote side determines the remote side's capacity information and transmission speeds for uplink and downlink, based on the capacity information and transmission speeds for uplink and downlink received from the center side at the second negotiation. As a third negotiation, the remote side transmits R-RATES2 and R-MSG2 to the center side, informing the capacity information and transmission speeds for uplink and downlink decided at the remote side. Upon receiving R-RATES2 and R-MSG2 from the remote side, the center side transmits the information with the same content as C-RATES2 and C-MSG2 to the remote side, if there is no change in the capacity information and transmission speeds for uplink and downlink decided at the second negotiation. And the center side declares that the communication will be performed with the capacity information, transmission speeds for uplink and downlink, and additive information determined by the center side.
Lastly, the center side transmits the capacity information, transmission speeds for uplink and downlink, and additive information declared at the third negotiation as C-B&G to the remote side. The remote side transmits the capacity information, transmission speeds for uplink and downlink, and additive information instructed by the center side as R-B&G to the center side.
As described above, the center and remote sides perform three negotiations, in which carrier number for carrier, bit allocation for each carrier, and B&G that sets gain information for the carrier are finally exchanged to be used, to complete the initialization sequence. Upon normally completing the initialization sequence, the data communication begins (SHOWTIME).
It takes about 10 to several tens of seconds for the above-described ADSL communication apparatus to start a data transmission (SHOWTIME) after the power is turned on. However, in a situation where the ADSL communication apparatus is connected to a personal computer via the USB, the power for the ADSL communication apparatus is cut off when the power to the personal computer is shut down. Therefore, every time a user turns on the power for the personal computer, an initialization sequence of the ADSL communication apparatus is performed, thus the user feels that the initialization sequence is taking a long time.